1. Field of the Invention
The present invention relates to a Lewis acid catalyst composition. More particularly, the present invention is concerned with a Lewis acid catalyst composition comprising a specific mixed medium and a Lewis acid catalyst which is a compound comprising a specific ligand, wherein the ligand contains a substituent selected from the group consisting of a perfluorinated, saturated or unsaturated C7–C20 hydrocarbon group containing in the skeleton thereof at least one heteroatom selected from the group consisting of a nitrogen atom and an oxygen atom and a partially substituted derivative of the above-mentioned C7–C20 hydrocarbon group. The Lewis acid catalyst composition of the present invention exhibits high catalytic activity by virtue of its improved solubility. By the use of the Lewis acid catalyst composition of the present invention for a Lewis acid-catalyzed reaction, after the reaction, not only can the Lewis acid catalyst be easily separated and recovered from the catalytic reaction mixture containing the same, but also the recycling of the Lewis acid catalyst can be performed without suffering the lowering of the catalytic activity. The present invention is also concerned with a method for continuously performing a reaction which proceeds in the presence of the above-mentioned Lewis acid catalyst by using the above-mentioned specific mixed solvent and the Lewis acid catalyst. Further, the present invention is also concerned with a novel Lewis acid catalyst.
2. Prior Art
A Lewis acid catalyst has been employed in various acid-catalyzed reactions for the synthesis of organic compounds. However, known Lewis acid catalysts, such as aluminum chloride, boron trifluoride and titanium tetrachloride, has problems in that the catalytic reaction systems are only limited to those in which the reactions proceed stoichiometrically and those in which the types of reaction solvents used are limited.
As a Lewis acid compound, a metal salt of a sulfonylimide or sulfonylmethide comprising a fluorine-substituted compound essentially having a polymerization-active species is disclosed in Canadian Patent No. 2,236,196 and this Lewis acid compound is used as a raw material for a membrane of a fuel cell. Further, an alkali metal salt or alkaline earth metal salt of a sulfonylimide or sulfonylmethide comprising a perfluoroalkyl group is disclosed in International Patent Application Publication No. WO 99/45048. In addition, an alkali metal salt or alkaline earth metal salt of a fluorine-substituted compound comprising a carbon-carbon double bond is disclosed in U.S. Pat. No. 5,463,005. A metal salt of a sulfonylimide comprising a perfluoroalkyl group is disclosed in Japanese Patent Application prior-to-examination Publication (Tokuhyo) No. 2001-526451. However, none of the above-mentioned patent documents describe that the metal salts disclosed therein, which are Lewis acid compounds, can be used as excellent Lewis acid catalysts having high catalytic activity. Further, these patent documents have no description about a Lewis acid catalyst composition which uses the Lewis acid compound and a fluorinated compound medium in combination.
Recently, Unexamined Japanese Patent Application Publication Nos. Hei 7-246338 and Hei 10-230167 disclose that a metal salt of a bis(perfluoroalkanesulfonyl)imide is an excellent Lewis acid catalyst having high catalytic activity. Further, Unexamined Japanese Patent Application Publication No. 2000-219692 discloses that a tris(perfluoroalkanesulfonyl)methide is an excellent Lewis acid catalyst.
In general, organometal complex catalysts are used so as to catalyze reactions which proceed in a homogeneous reaction system and, therefore, the use of such catalysts in the catalytic reaction system has a problem in that, in the commercial practice of the catalytic reaction, after the reaction, the separation and recovery of the catalyst from the reaction mixture and the recycling of the recovered catalyst are accompanied with difficulties.
For solving such a problem, a number of proposals have been made with respect to methods for separating and recovering a Lewis acid catalyst employed in a reaction. As an example of the methods, there can be mentioned a method in which a Lewis acid catalyst is immobilized. For example, a study has been made about the method which comprises fixing a catalyst to an inorganic or macromolecular carrier to thereby obtain an immobilized catalyst, and effecting a solid phase synthetic reaction by dispersing the obtained immobilized catalyst in the reaction system.
Although the immobilized catalyst can be easily recovered from the synthetic reaction system, the solid phase synthetic reaction has problems in that not only is the catalytic activity lowered, but also the solid phase synthetic reaction is not applicable to all of the organic syntheses which are generally conducted in a homogeneous liquid phase. Therefore, it has been desired to develop a technique which is advantageous not only in that a reaction efficiency in a liquid phase is increased, and a post-treatment of the reaction mixture can be done simply, but also in that the catalyst used can be easily recovered and recycled. It has especially been desired to develop a method for separation, recovery and recycling of a Lewis acid catalyst, which can be widely used for various acid-catalyzed reactions.
In this situation, in Unexamined Japanese Patent Application Publication No. 2001-190962, the present inventors disclosed a Lewis acid catalyst composition for use in an acid-catalyzed reaction. In this patent document, a Lewis acid-catalyzed reaction is performed in a mixed medium comprising a perfluorinated hydrocarbon and a non-fluorinated hydrocarbon and, then, the Lewis acid catalyst is recovered and recycled by the phase separation of the resultant reaction mixture. Although this method enables the recovery and recycling of the used catalyst, this method has the following problems. When a Lewis acid catalyst reaction is performed using the Lewis acid catalyst composition of the above-mentioned patent document, due to the relatively low rate of phase separation of the reaction mixture, a lowering of the productivity is caused, so that complicated apparatuses become necessary for performing the reaction in a continuous manner, and costs for the apparatuses become high. Therefore, it has been desired to develop a Lewis acid catalyst composition and a Lewis acid catalyst which are advantageous from the viewpoint of improvement in not only the recovery of the used catalyst, but also the yield of the reaction product.